A study on sheet metal hole-flanging process

Available online at www.sciencedirect.com ScienceDirect Materials Today: Proceedings 4 (2017) 5421–5428 www.materialstoday.com/proceedings 6th International Conference of Materials Processing and Characterization (ICMPC 2016) A study on sheet metal hole-flanging process Yogesh Dewang1*, Rajesh Purohit2 and Nitin Tenguria3 1*Assistant Professor, Department of Mechanical Engineering, Lakshmi Narain College of Technology, Bhopal, 462021, India) Associate Professor, Department of Mechanical Engineering, Maulana Azad National Institute of Technology, Bhopal, 462003, India) 3Associate Professor, Department of Mechanical Engineering, Sagar Institute of Research & Technology, Bhopal, 462041, India) 2 Abstract Hole-flanging is a manufacturing process which is used to form flanges around holes by using sheet metal. A brief and concise review of the contributions made by the previous researchers in the area of hole-flanging process has been presented. Steel sheet material and aluminum alloys are used by researchers for hole flange forming. FEM modelling of hole-flanging is carried out by employing axisymmetric conditions. Meshing of the work piece is done by using axisymmetric quadrilateral elements. Experimental set-up and tools utilized in formation of hole flanges are presented and discussed. Results are presented in terms of variation of distribution of thickness along flange wall through conventional hole-flanging and incremental forming technique. Incremental forming techniques with different forming strategies is found to be more accurate, less complicated and better means of hole flanging in comparison to conventional forming techniques. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 6th International Conference of Materials Processing and Characterization (ICMPC 2016). Keywords:Hole flanging; flange; finite-element;incremental; conventional;sheet metal. 1. Introduction Hole-flanging is a sheet metal forming process which is widely used in automotive industry. It is another kind of flanging process which involves stretching and provides rigidity to hole flange. Practical applications of hole flangesinclude locating bosses, holes for tapped threads, openings for heat transfer tubes, non-chafing tubes and assembly with other mating parts. It is a process which flanges are formed by using a circular blank with a preformed hole to * Corresponding author. Tel: +91-0755-4051610;fax: +91-0755-2457042. E-mail address:[email protected]; [email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of 6th International Conference of Materials Processing and Characterization (ICMPC 2016). 5422 Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 increase the bearing surface or to increase the number or threads that will fit in a tapped hole. This process usually comprises of axisymmetric die, punch and blank holder.Fig.1 shows the schematic representation of conventional hole flanging process without ironing on left half of the figure whereas on the right half of the figure represents the hole flanging with ironing. Hole flanging process can be performed with or without ironing. As shown in the below Fig 1. In case of hole-flanging without ironing, sheet is restricted between die and blank-holder by application of suitable blank-holding force. In this case hole flange is formed due to stretching of edge resulting into thinning of flange. On the other hand, hole flanging with ironing can be performed by adjusting a low value of clearance between the punch and die. Through this process, metal is compressed between punch and die, which give rise to longer flanges. Besides conventional hole flanging process with ironing and without ironing, there is another form in which hole flanging can be performed is known as incremental hole flange forming. Incremental forming is new technology of forming which do not requires conventional set of tools such die, blank-holder and punch. In this technology, it requires only one holding device and one forming tool as compared to the need to have multistage stamping dies and punches for different forming stages in traditional metal forming processes.Fig.2 shows the schematic representation of the incremental hole flanging process. A flat sheet with a pre-cut hole is clamped onto a forming fixture that is mounted onto the table of a three-axis CNC machine. The forming tool which is mounted to the spindle travels along a CNC tool path and incrementally forms the open area of the blank into a flange. In past, various researchers contributed in the area of hole-flanging process. Leu [1] conducted finite element simulation of a hole-flanging operation on a flat circular sheet with a hole in the centre by an incremental elastoplastic finite element method, which incorporates strain-hardening and anisotropy in the direction normal to the sheet. Kumagai and Saiki [2] investigated the characteristics of hole flanging with ironing of thick sheet of commercially pure aluminum by FE simulation and experimentally. Zainullin and Saginbaev [3] proposed a new design of branch pipe in order to increase the load-carrying capacity of the triple-joint in hole-flanging process. Kumagai et al. [4] studied the forming characteristics in hole-flanging with ironing for two-ply sheet metals. Huang and Chien [5] employed the incremental updated lagrangian elasto-plastic method finite element method (FEM) to analyze the hole-flanging of circular plates with a predetermined similar hole at the centre of the sheet metal. Huang [6] utilized an incremental updated Lagrangian elasto-plastic finite element method (FEM) to analyze the stretch flanging of circular plates of low-carbon (BA-CQ2) sheet plate with a thickness of 1.0 mm and pre-determined smaller hole.Chen [7] developed a three-dimensional elasto-plastic finite element model for simulation of hole-flanging process and found that maximum reduction in wall thickness occurs on the end of expanded elliptic hole. Fig.1 Conventional hole-flanging process [14] Fig.2. Three tool paths are used in incremental hole-flanging process [21] Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 5423 Min et al.[8] employed grey relational analysis for optimizing the square hole-flanging process parameters with considerations of the multiple responses (the average flanging height, regular flanging and maximum strain).Thipprakmas et al. [9] carried out FE simulation in order to predict the deformations occurring during the FB-hole-flanging process. Stachowicz [10] presented some experimental results of hole-flanging process performed on flat deep drawing steel sheets with circular hole drilled in the centre and studied the effect of three punches of different geometry i.e. cylindrical, hemispherical and conical and material mechanical parameters (especially strain hardening and plastic anisotropy) on the limit expansion of the hole by performing experiments. Elbitar and Gemeal [11] carried out finite element analysis of an oil filter cover which contains outer flange processed by deep drawing and inner flange processed by hole-flanging. Li et al. [12] carried out finite element simulation of hole-flanging process and established the relationship between punch load and punch stroke, the variation of the work piece thickness, and the forming limit.Nepershin [13] presented a model of axisymmetric formation of a flange from a flat blank with a hole by expanding by a hard punch with a fixed flat flange. Kacem et al. [14] investigated the effect of the clearance-thickness ratio on the hole-flanging process in order to determine the occurrence of ironing. Krichen et al.[15] investigated the effect of blank-holding force on the hole-flanging process using numerical and experimental analysis of a commercial aluminum alloy with a thickness of 2 mm. Petek and Kuzman[16] proposed a modern manufacturing known as backward incremental hole-flanging process and found that the proposed technology has three significant process parameters affecting the neck height and thickness distribution, i.e. forming tool diameter, horizontal step size and vertical step size.Shrivastava et al. [17]developed a finite element simulation model for hole flanging process in order to predict lip shape behavior of advanced high strength steel and studied the effect of varying geometrical conditions such as thickness of the sheet, punch and die gap and center hole diameter on lip shape behavior.Lin et al. [18] proposed a novel hole-flanging method for thick plate through upsetting process. Bambach et al. [19] devised a new process design for performing hole-flanging through incremental flanging. Cristino et al. [20] demonstrated the differences in deformation mechanics of hole-flanging by single point incremental forming technique. Cui and Gao [21] studied hole-flanging with incremental forming technique with different forming strategies.The objective of this research paper is to review various aspects of hole flanging process in terms of materials used, FEM modelling and simulation and experimental setup and procedure applied. Difference between conventional and incremental hole-flanging process is also discussed herein through presentation of few common variables results. 2.Overview of hole-flanging process 2.1 Materials utilized in hole -flanging process Flanges are certainly made to support the assembly with other mating parts. For performance of such application, the flange material is of prime importance. Flanges are usually made of various grades of steel. Table 1 shows the description of the authors who have used variety of materials as workpiece material for manufacturing of hole flanges. It is clear from Table 1 that in majority of the cases, researchers have used steel sheets. In some cases, they have also used different aluminum alloy sheet metal for formation of hole flanges. Table 1.Sheet metal used for workpiece by previous researchers Author Leu [1] Year 1996 Material Steel sheet Zainullin and Saginbaev[3] 1998 17GIS type steel Kumagai et al.[4] 1999 Welded Al:Cu bi-metallic sheet metal Huang [6] 2007 low carbon Steel sheet (BA -CQ2) Min et al.[8] Krichen et al.[15] Kacem et al.[14] Petek and Kuzman[16] Shrivastava et al. [17] 2007 2011 2011 2012 2013 Pure aluminum sheet (L2) Aluminum alloy sheet 1000 series aluminum alloy sheet DC05 steel Advanced High strength steel 5424 Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 2.2 FEM modelling of hole -flanging process In order to better designing of the hole-flanging process as well as to obtained defect free products, finite element modelling and simulation is a numerical technique which is popularly used by researchers in past. Krichen et al. [15] developed an axisymmetric finite element model for hole flanging process in which they had utilized 3-noded linear axisymmetric triangle hybrid constant pressure element (CAX3H) for meshing of elastic annular ring and modelled sheet metal blank (workpiece) by using 4-nodes bilinear axisymmetric quadrilateral element with selective reduced integration (CAX4R) and (CAX3H). Fig.3. Mesh and geometrical parameters of the hole-flanging process[15] Fig. 4.The profile of the punch and die[7]Fig. 5.The mesh of blank in elliptic hole-flanging forming simulation[7] They have utilized an updated formulation of the mesh due to the large strain level in hole-flanging process. Fig.3 shows the half finite element meshed model of an axisymmetric hole flanging process. Chen [7] used the elasto- Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 5425 plastic large deformation 3-D finite element method to perform FEM analysis of elliptic hole-flanging process. Fig.4 shows the profiles of punch, holder, die and workpiece. He developed a full 3D model of punch, die, holder and workpiece by using CAD software. During FEM simulation he understood the symmetry of the model and meshed only quarter portions of workpiece and tools. He used a four-node rectangular shell element for meshing of workpiece while triangular elements are utilized for meshing of tools. Fig.5 shows rectangular elements when the blanks are meshed. 2.3 Experimental set-up of hole- flanging process Krichen et al. [15] developed a whole experimental set-up which comprises of circular workpiece with pre-cut hole in the centre, load cell and tools as shown in fig.6. The experiments of conventional hole-flanging are carried out on a universal traction-compression testing machine. The experimental set-up is designed in such a manner that different categories of blank-holding forces (fixed-blank holder, without blank-holder, constant force on bank-holder and progressive force of different trajectories) can be developed and applied. They have used series of springs having different stiffness to produce different progressive blank holding forces. They have also realized the condition of without blank holding force by removing blank-holder from the tool whereas they have placed workpiece between the die and blank-holder and clamped assembly with two M10 bolts. The results of devices such as displacement gauge and of load cell are recorded continuously in a data acquisition system. Kacem et al. [14] developed experimental set-up for carrying hole-flanging experiments with and without the effect of ironing. Fig.6. The profile of the punch and die[15] Fig.8. Schematic representation of incremental hole-flanging [21] Fig.7. Experiemental tools for hole flanging[14] Fig.9. Die layout used in experiments[9] 5426 Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 Fig.7 shows the experimental set-up for hole-flanging experiments having circular workpiece with pre-cut hole and tools such as truncated pilot-punch die and blank-holder. The workpiece is placed between die and blank-holder and tightened it with four M10 bolts in a similar manner as employed by Krichen et al. [15].Cui and Gao [22] conducted the experiments of hole-flanging process with three stage incremental forming technology. Fig. 8 shows the schematic of the incremental hole-flanging process. They utilized a flat sheet with a pre-cut hole which is placed onto a forming fixture and this whole assembly is fixed on the table of CNC machine. Incremental technique is utilized herein for formation of flange in stages as a forming tool connected to the spindle moves along a CNC tool path. Thipprakmas et al. [9]conducted experiments of fine-blanked hole flanging process by 4000 kN fine blanked press machine with a facility of setting of blank holding force counterpunch force. Fig.9 shows the layout of the die and tools used in the fine-blanked hole-flanging process. They performed the experiments of fine-blanked holeflanging process in three different steps i.e punching, flange formation and blanking. The hole flange is formed in second stage on strip material sheet. It is found that multistage incremental forming techniques provides better facility ofcompact experimental set-up(only one clamping deviceand one forming tool) for formation of hole flange in comparison to conventional hole-flanging process, which requires very complicated and dedicated sort of experimental set-up and tools. 2.4 Products obtained after hole-flanging Chen [7] conducted experiments of elliptic hole-flanging process at a EFR = 1.6511 (major radius = 20 mm , minor radius = 9 mm).He found that fracture occurs around the expanded elliptic periphery when the initial radius of blank is 20 mm and 9 mm as shown in fig. 10(a). Krichen et al.[15] conducted experiments of hole-flanging of aluminum alloys considering different blank holding forces and obtained typical finished shape of hole flange as shown in fig.10(b). Thipprakmas et al. [9] demonstrated an example of hole flange as an automotive part as shown in fig.10(c). Fig.10. Products after hole flanging operation (a) Elliptic hole flange with fracture [7] (b) hole –flange without fracture[15] (c) hole flange (automotive part)[9] Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 5427 3. Results and discussion Variation in thickness along the flange wall is the vital result which decides the formability of hole flanges. Fig. 11(a) shows the distribution of thickness along major axis of the sheet for formation of hole flange as found by Chen et al. [7] in elliptic hole flanging process. Chen et al. [7] found that the maximum reduction in blank thickness occurred on the end of major axis direction and diminishes gradually after a position near the centre of major axis and finally falls below initial thickness towards sheet centre. Another case of hole-flanging process, deals with the employment of multistage incremental forming technique. Fig.11 (b) shows the variation of wall thickness profile with increase in neck height of hole-flange using five stages of incremental forming. Cui and Gao et al. [21] found that the thickness decreases with increase in neck height of hole flange and then again increases again due to excessive reduction in sheet thickness. They also found that the fracture of part will occur at location of minimum thickness after the thinning limit of sheet is exceeded. They alsoreported that multistage incremental forming technique process provides benefits such as easy control over shape and dimensional accuracy by varying parameters such as pitch of tool path, tool diameter and formingspeedas compared to conventional hole-flanging. Besides this, they also found that a higher forming limit can be achieved in incremental forming as compared to conventional forming processes. Fig.11 (a) Thickness distribution along major axis of elliptic hole flanging process[7] Fig. 11(b) Variation of part thickness with neck height with 5stages incrmental forming technique [21] 4. Conclusions In the body of work presented in this paper, hole-flanging process is studied by considering various aspects of hole-flanging process. A brief and concise review of the contributions made by the previous researchers in the area of hole-flanging process is also presented. It is found that researchers have utilized steel sheet material for formation of hole flanges as workpiece material in majority of cases, however in the recent past, the usage of aluminum alloy has also been started. It has also been found that researchers carried out FEM modelling of hole-flanging process by employing axisymmetric conditions and modelled problem with half and quarter geometry. Meshing of the workpiece is done by using axisymmetric quadrilateral elements. It is also found that the incremental forming technique requires a compact experimental set-up and tools in comparison to traditional forming techniques of holeflanging. It is also concluded that higher forming limit is obtained with incremental forming technique with added advantages of better dimensional accuracy and control over shape. Hence through this study it is concluded that incremental forming using different stages is better forming technique over conventional forming technique of holeflanging process. 5428 Yogesh Dewang et al./ Materials Today: Proceedings 4 (2017) 5421–5428 5. Future work In this area of hole-flanging process, future work can be considered by taking sheet metal with nickel coatings. The preparation of this workpiece material can be done through rolling of metals and through powder metallurgy. After preparation of this workpiece material, this material can be formed by using hole-flanging technique. The experimental work includes formation of hole flanges using above prepared material by using conventional forming as well as incremental forming technique. A comparative study of formability of hole flange both by conventional and incremental technique is the area of concern of this proposed work in future. References [1] Leu D W.Finite element simulation of hole flanging process of circular sheets of anisotropic material. Int J Mech Sci 2014; 38 (8-9): 917-933. [2] Kumagai T, Saiki H. Deformation analysis of hole flanging with ironing of thick sheet metals. Metals Mater 1998; 4(4): 711-714. [3] Zainullin R S, Saginbaev R K. Using stamped-welded straps with flanged branch pipes in operating pipelines. Chem Petrol Eng 1998; 34(78):537-539. [4] Kumagai T, Saiki, Meng Y. Hole flanging with ironing of two-ply thick sheet metals. J Mater Process Tech 1999; 89-90(1):51-57. [5] Huang Y M, Chien K H.The formability limitation of the hole flanging process. 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